Download Animal Physiology, Chapter 23

The heart circulates blood to every tissue and organ, sustaining all bodily strength
Functions of the Circulatory System
• Transportation:
– Respiratory:
• Transport 02 and C02.
– Nutritive:
• Carry absorbed digestion products to liver and
to tissues.
– Excretory:
• Carry metabolic wastes to kidneys to be
excreted.
Functions of the Circulatory System
(continued)
• Regulation:
– Hormonal:
• Carry hormones to target tissues to produce their effects.
– Temperature:
• Divert blood to cool or warm the body.
– Protection:
• Blood clotting.
– Immune:
• Leukocytes, cytokines and complement act against
pathogens.
Components of Circulatory System
• Components of Cardiovascular system
(CV):
– Heart:
• Pumping action creates pressure head needed to
push blood through vessels.
– Blood vessels:
• Permits blood flow from heart to cells and back to the
heart.
– Arteries, arterioles, capillaries, venules, veins.
• Lymphatic System:
– Lymphatic vessels transport interstitial fluid.
• Lymph nodes cleanse lymph prior to return in venous
blood.
Components of Whole Blood
Figure 17.1
Composition of Blood
• Composition of blood
• Plasma:
– Straw-colored liquid.
• Consists of H20 and dissolved solutes.
– Ions, metabolites, hormones, antibodies.
» Na+ is the major solute of the plasma.
• Plasma proteins:
– Constitute 7-9% of plasma.
• Albumin:
– Accounts for 60-80% of plasma proteins.
– Provides the colloid osmotic pressure needed to draw H20
from interstitial fluid to capillaries.
» Maintains blood pressure.
Composition of the Blood
• Composition of blood:
• Plasma proteins (continued):
(continued)
– Globulins:
 a globulin:
– Transport lipids and fat soluble vitamins.
 b globulin:
– Transport lipids and fat soluble vitamins.
 g globulin:
– Antibodies that function in immunity.
• Fibrinogen:
– Constitutes 4% of plasma proteins.
– Important clotting factor.
• Converted into fibrin during the clotting process.
Composition of the Blood
(continued)
• Composition of blood
• Serum:
– Fluid from clotted blood.
• Does not contain fibrinogen.
• Plasma volume:
– Number of regulatory mechanisms in the
body maintain homeostasis of plasma
volume.
• Osmoreceptors.
• ADH.
• Renin-angiotensin-aldosterone system.
Blood Cells and Platelets
• Erythrocytes
Erythrocytes
– Flattened biconcave discs.
– Provide increased surface area through which
gas can diffuse.
– Lack nuclei and mitochondria.
• Half-life ~ 120 days.
– Each RBC contains 280 million hemoglobin
with 4 heme chains (contain iron).
– Removed from circulation by phagocytic cells
in liver, spleen, and bone marrow.
• Leukocytes:
Leukocytes
– Contain nuclei and mitochondria.
– Move in amoeboid fashion.
• Can squeeze through capillary walls (diapedesis).
– Almost invisible, so named after their staining
properties.
• Granular leukocytes:
– Help detoxify foreign substances.
» Release heparin.
• Agranular leukocytes:
– Phagocytic.
» Produce antibodies.
• Platelets (thrombocytes)
Platelets (thrombocytes)
– Smallest of formed elements.
• Are fragments of megakaryocytes.
• Lack nuclei.
– Capable of amoeboid movement.
– Important in blood clotting:
• Constitute most of the mass of the clot.
• Release serotonin to vasoconstrict and reduce
blood flow to area.
– Secrete growth factors:
• Maintain the integrity of blood vessel wall.
– Survive 5-9 days.
Hematopoiesis
• Hematopoiesus
– Undifferentiated cells gradually differentiate to
become stem cells, that form blood cells.
– Occurs in myeloid tissue (bone marrow of long
bones) and lymphoid tissue.
– 2 types of hematopoiesis:
• Erythropoiesis:
– Formation of RBCs.
• Leukopoiesis:
– Formation of WBCs.
Figure 23.1 The human heart
Figure 23.14 The circulatory plan in gill-breathing fish (Part 2)
Figure 23.22 Circulation through the body of a crayfish or lobster (Part 1)
Figure 23.18 Blood flow in heart ventricles and systemic and pulmonary arteries of crocodilians
Pulmonary and Systemic Circulations
• Pulmonary circulation:
– Path of blood from right
ventricle through the
lungs and back to the
heart.
• Systemic circulation:
– Oxygen-rich blood
pumped to all organ
systems to supply
nutrients.
• Rate of blood flow
through systemic
circulation = flow rate
through pulmonary
circulation.
Figure 23.10 The circulatory plan in mammals and birds (Part 1)
Figure 23.10 The circulatory plan in mammals and birds (Part 2)
Figure 23.14 The circulatory plan in gill-breathing fish (Part 1)
Figure 23.15 The circulatory plans of some air-breathing fish (Part 1)
Figure 23.15 The circulatory plans of some air-breathing fish (Part 2)
Figure 23.16 The branchial vascular arches of a lungfish
Figure 23.19 The circulatory plan of squids and octopuses (Part 1)
Figure 23.22 Circulation through the body of a crayfish or lobster (Part 2)
Box 23.3 Blood flow through the tissues of an insect is principally through lacunae and sinuses
Conducting Tissues of the Heart
• Contracting tissues of the heart:
– APs spread through myocardial cells through gap
junctions.
– Impulses cannot spread to ventricles directly because
of fibrous tissue.
– Conduction pathway:
•
•
•
•
SA node.
AV node.
Bundle of His.
Purkinje fibers.
– Stimulation of Purkinje fibers cause both ventricles to
contract simultaneously.
Conducting Tissues of the Heart
(continued)
Conduction of Impulse
• Conduction of impulse
– APs from SA node spread quickly at rate of
0.8 - 1.0 m/sec.
– Time delay occurs as impulses pass
through AV node.
• Slow conduction of 0.03 – 0.05 m/sec.
– Impulse conduction increases as spread to
Purkinje fibers at a velocity of 5.0 m/sec.
• Ventricular contraction begins 0.1–0.2 sec. after
contraction of the atria.
Refractory Periods
• Refractory periods:
• Heart contracts as
syncytium.
• Contraction lasts
almost 300 msec.
• Refractory periods
last almost as long
as contraction.
• Myocardial muscle
cannot be
stimulated to
contract again until
it has relaxed.
– Summation cannot
occur.
Electrocardiogram (ECG/EKG)
• EKG (ECG)
• The body is a good conductor of electricity.
– Tissue fluids have a high [ions] that move in
response to potential differences.
• Electrocardiogram:
– Measure of the electrical activity of the heart per
unit time.
• Potential differences generated by heart are conducted
to body surface where they can be recorded on
electrodes on the skin.
• Does NOT measure the flow of blood through
the heart.
ECG Leads
• ECG leads
• Bipolar leads:
– Record voltage between
electrodes placed on wrists
and legs.
– Right leg is ground.
• Unipolar leads:
– Voltage is recorded between
a single “exploratory
electrode” placed on body
and an electrode built into the
electrocardiograph.
– Placed on right arm, left arm,
left leg, and chest.
• Allow to view the changing
pattern of electrical activity
from different perspectives.
Figure 23.4 The conducting system and the process of conduction in the mammalian heart (Part 1)
Figure 23.4 The conducting system and the process of conduction in the mammalian heart (Part 2)
Figure 23.4 The conducting system and the process of conduction in the mammalian heart (Part 3)
Figure 23.6 Electrocardiography (Part 1)
ECG
• P wave:
– Atrial
depolarization.
• QRS
complex:
– Ventricular
depolarization.
– Atrial
repolarization.
• T wave:
– Ventricular
repolarization.
Figure 23.6 Electrocardiography (Part 2)
Figure 23.6 Electrocardiography (Part 3)
Figure 23.2 The heart as a pump: The dynamics of the left side of the human heart
Figure 23.2 The heart as a pump: The dynamics of the left side of the human heart (Part 1)
Cardiac Cycle
(continued)
• Step 1: Isovolumetric contraction:
– QRS just occurred.
– Contraction of the ventricle causes ventricular pressure to
rise above atrial pressure.
• AV valves close.
– Ventricular pressure is less than aortic pressure.
• Semilunar valves are closed.
– Volume of blood in ventricle is EDV.
• Step 2: Ejection:
– Contraction of the ventricle causes ventricular pressure to
rise above aortic pressure.
• Semilunar valves open.
– Ventricular pressure is greater than atrial pressure.
• AV valves are closed.
– Volume of blood ejected: SV.
Cardiac Cycle
(continued)
• Step 3: T wave occurs:
– Ventricular pressure drops below aortic pressure.
• Step 4: Isovolumetric relaxation:
– Back pressure causes semilunar valves to close.
• AV valves are still closed.
– Volume of blood in the ventricle: ESV.
• Step 5: Rapid filling of ventricles:
– Ventricular pressure decreases below atrial pressure.
• AV valves open.
– Rapid ventricular filling occurs.
Figure 23.2 The heart as a pump: The dynamics of the left side of the human heart (Part 2)
Figure 23.3 Four systems evolved by animals to supply O2 to the myocardium (Part 1)
Figure 23.3 Four systems evolved by animals to supply O2 to the myocardium (Part 2)
Figure 23.7 Fluid-column effects on blood pressure in the arterial vascular system
Figure 23.8 Total fluid energy: The true driving force for blood flow
Figure 23.9 The physics of flow through tubes
Figure 23.11 A microcirculatory bed
Figure 23.12 Blood flow in the human systemic vasculature (Part 1)
Figure 23.12 Blood flow in the human systemic vasculature (Part 2)
Figure 23.13 Fluid exchange across mammalian systemic capillary walls
Maintaining Blood Pressure
• Maintaining blood pressure requires:
– Cooperation of the heart, blood vessels, and
kidneys
– Supervision of the brain
Maintaining Blood Pressure
• The main factors influencing blood
pressure are:
– Cardiac output (CO)
– Peripheral resistance (PR)
– Blood volume
• Blood pressure = CO x PR
• Blood pressure varies directly with CO,
PR, and blood volume
Cardiac Output (CO)
• Cardiac output is determined by venous
return and neural and hormonal controls
• Resting heart rate is controlled by the
cardioinhibitory center via the vagus
nerves
– Stroke volume is controlled by venous return
(end diastolic volume, or EDV)
• Under stress, the cardioacceleratory
center increases heart rate and stroke
volume
– The end systolic volume (ESV) decreases and
MAP increases
Frank-Starling Law
Cardiac Output (CO)
Figure 19.7
Controls of Blood Pressure
• Short-term controls:
– Are mediated by the nervous system and
bloodborne chemicals
– Counteract moment-to-moment fluctuations in
blood pressure by altering peripheral
resistance
• Long-term controls regulate blood volume
Short-Term Mechanisms: Neural Controls
• Neural controls of peripheral resistance:
– Alter blood distribution in response to demands
– Maintain MAP by altering blood vessel diameter
• Neural controls operate via reflex arcs involving:
– Baroreceptors
– Vasomotor centers and vasomotor fibers
– Vascular smooth muscle
Short-Term Mechanisms: Vasomotor Activity
• Sympathetic activity causes:
– Vasoconstriction and a rise in BP if increased
– BP to decline to basal levels if decreased
• Vasomotor activity is modified by:
– Baroreceptors (pressure-sensitive),
chemoreceptors (O2, CO2, and H+ sensitive),
higher brain centers, bloodborne chemicals,
and hormones
Short-Term Mechanisms: Baroreceptor-Initiated Reflexes
• Increased blood pressure stimulates the
cardioinhibitory center to:
– Increase vessel diameter
– Decrease heart rate, cardiac output,
peripheral resistance, and blood pressure
Short-Term Mechanisms: Baroreceptor-Initiated Reflexes
• Declining blood pressure stimulates the
cardioacceleratory center to:
– Increase cardiac output and peripheral
resistance
• Low blood pressure also stimulates the
vasomotor center to constrict blood
vessels
Baroreceptor Reflex
(continued)
Regulation by ADH
• Released by
posterior pituitary
when osmoreceptors
detect an increase in
plasma osmolality.
• Dehydration or
excess salt intake:
– Produces sensation
of thirst.
– Stimulates H20
reabsorption from
urine.
Chemicals that Decrease Blood Pressure
• Atrial natriuretic peptide (ANP) – causes
blood volume and pressure to decline
• Nitric oxide (NO) – is a brief but potent
vasodilator
• Inflammatory chemicals – histamine,
prostacyclin, and kinins are potent
vasodilators
• Alcohol – causes BP to drop by inhibiting
ADH
Long-Term Mechanisms: Renal Regulation
• Long-term mechanisms control BP by
altering blood volume
• Baroreceptors adapt to chronic high or low
BP
– Increased BP stimulates the kidneys to
eliminate water, thus reducing BP
– Decreased BP stimulates the kidneys to
increase blood volume and BP
Kidney Action and Blood Pressure
• Kidneys act directly and indirectly to
maintain long-term blood pressure
– Direct renal mechanism alters blood volume
– Indirect renal mechanism involves the reninangiotensin mechanism
Kidney Action and Blood Pressure
– Declining BP causes the release of renin,
which triggers the release of angiotensin II
– Angiotensin II is a potent vasoconstrictor that
stimulates aldosterone secretion
– Aldosterone enhances renal reabsorption and
stimulates ADH release
Renin-Angiotension-Aldosterone System
(continued)
Diving physiology part 1
• The oxygen store of divers
– Adjustment of circulatory function
• CNS and heart dependent on aerobic catabolism
for ATP production
• Skeletal muscle tolerant of O2 deprivation
• Blood flow to skin, gut, kidneys is curtailed by
vasoconstriction
• Oxygen deprived tissue will turn to anaerobic
catabolism
– Lactic acid accumulates
Diving physiology part 2
• The amount of O2 stored in blood depends
on:
– O2 carrying capacity of the blood
– Volume of blood
– Degree of saturation of blood with O2 at the
time of submergence
Diving physiology
• Thoracic cavity and lungs-- compressible
• High myoglobin concentrations
– In skeletal muscle
– Large myoglobin-bound O2 stores
– O2 remains bound to the myoglobin until the
O2 partial pressure in the muscles falls to a
low level
Circulatory adjustment during dives
• Bradycardia
– Drop in cardiac output
– Weddell seals show an 86% drop in cardiac work and
an 85% reduction in blood flow to their ventricular
heart muscle
• Regional vasoconstriction
– Becomes a “heart-lung-brain” machine
– Large concentration of rbcs in their blood when they
are diving
– Rbcs stored in their spleen- release during dive
Metabolism during dives
• 3 factors determine the limits of endurance of
the O2 –dependent tissues
– Magnitude of O2 store available
– Rate of use of the O2 store
– Extent to which P02 can fall before impairing the
function of O2-dependent tissues
• MR during dive is the most important factor in
determining metabolic limits on dive duration
– low MR, slow O2 depletion, and slow lactic acid
accumulation
The aerobic dive limit
• Prolong dive has major behavioral
consequences
– Requires time for ridding body of lactic acid
– Must stay at the water’s surface where it can
breathe
– Lactic acid burdens of successive dives
• Additive
• Example- a seal that accumulates 80 ml lactic
acid/ 100 ml of blood has to remain at the surface
over an hour to return its lactic acid to resting level
Decompression sickness (DS)
• Caused by N2 absorption from a compressed-air
source
– Start of dive– tissue contains a [N2]
• DS occur after a long deep dive and then
surfaces suddenly
– PN2 pressure falls in the lungs to its ordinary value
– N2-charged blood and other tissues start to lose N2 in
the lung air
– Bubbles of blood may form within the blood and
tissues
Decompression sickness (DS) 2
• Breath-hold dives must be repeated many
times to cause DS in humans
• Marine animals avoid DS during deep
dives by alveolar collapse
– Special features of lungs and thorax
• Keep pulmonary N2 within lungs
• Avoid build up in blood and tissues
• Lung air moves to conducting airways